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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Primary rat hepatocytes were transfected with simian virus 40 DNA and cultured in a chemically defined medium. Proliferating colonies developed after 2-3 weeks. Three cell lines were established by cloning albumin-secreting colonies, as identified by an immunooverlay assay. Two of the cell lines, ALB-6 and ALB-8, expressed all five liver-specific mRNAs studied, albumin, alpha-1-antitrypsin, fibrinogen, alpha-1-acid glycoprotein, and histidase. ALB-6 cells were nontumorigenic in nude mice while ALB-8 cells were weakly tumorigenic with only one of four injected nude mice developing a slowly growing tumor. Further transfection of ALB-6 and ALB-8 cells with an activated c-Ha-ras or N-ras oncogene resulted in strongly tumorigenic cells. The tumors induced by ras-transformed ALB-6 cells were moderately differentiated hepatocellular carcinomas. The tumors derived from ras-transformed ALB-8 cells were poorly differentiated, while the slowly growing tumors induced by untransfected or control DNA-transfected ALB-8 cells were well-differentiated trabecular hepatocellular carcinomas, suggesting histological dedifferentiation of cells following ras transformation. However, the synthetic capabilities of the cells were not lost in that the ras-transfected cultures and the tumors induced by ras-transformed cells retained the ability to synthesize the five liver-specific mRNAs. Thus we have developed an in vitro model of carcinogenesis in which, by sequential exposure to SV40 DNA and a ras oncogene, primary rat hepatocytes are transformed.
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PMID:ras transformation of simian virus 40-immortalized rat hepatocytes: an in vitro model of hepatocarcinogenesis. 130 23

The frequency and pattern of mutations at codon 61 of the c-Ha-ras protooncogene were analysed in glucose-6-phosphatase-deficient hepatic lesions of male C3H/He mice occurring either spontaneously or after continuous treatment with 10 p.p.m. dieldrin or 500 p.p.m. phenobarbital (PB) in their diet. At 52 weeks after start of promoter administration, enzyme-altered liver lesions had developed in 41% (15/37) of untreated control mice and in 67% (10/15) and 63% (10/16) of mice treated with dieldrin or PB respectively. The average numbers of focal lesions per mouse were 0.57 in the control, 1.5 in the dieldrin and 1.0 in the PB group. Lesions were punched out from frozen liver sections and used for mutation analysis by allele-specific oligonucleotide hybridization following in vitro amplification of DNA via polymerase chain reaction. In the control group, 12 out of 21 liver lesions (57%) showed c-Ha-ras mutations, while five out of 23 (22%) and four out of 16 (25%) lesions were mutated in the dieldrin and PB groups. Taking the different numbers of animals in the three experimental groups into account, our data indicate that the tumour promoters increased the frequency of c-Ha-ras wild-type but not of c-Ha-ras mutated focal liver lesions, suggesting that the mutations had occurred spontaneously and were not related to treatment. Since c-Ha-ras mutations were found to be frequent in large but infrequent in small hepatocellular lesions, these mutations may represent in livers of C3H/He mice an endogenous promoting principle that provides a selective growth advantage to the mutated progenitor cells.
Carcinogenesis 1992 Mar
PMID:The tumour promoters dieldrin and phenobarbital increase the frequency of c-Ha-ras wild-type, but not of c-Ha-ras mutated focal liver lesions in male C3H/He mice. 131 98

To analyze the role of human papillomavirus (HPV) infection and c-myc and c-Ha-ras oncogene activation in cutaneous and mucosal lesions, serial frozen sections of 47 lesions from grafted recipients and 10 biopsies from non-immunosuppressed patients were examined. HeLa, CaSki, MCF7, Colo 320 and 3T3 cells, which contain various copy numbers of HPV DNA and/or c-myc gene, were used as controls. HPV, myc and ras oncogene DNAs were not detected in normal epithelia by in situ hybridization with biotinylated DNA probes. The amplification of ras oncogene was detected in 20/57 lesions. The amplification of myc oncogene was found in 14/57 lesions, 13 of which showed both myc and ras gene amplification. c-myc and/or c-Ha-ras DNA was more frequently amplified in cutaneous squamous cell carcinomas (8/14 cases) and anogenital papillomas (4/6 cases), than in common and plantar warts (3/14 cases) or actinic keratoses (2/10 cases). HPV DNA was detected in 26/57 biopsies. Oncogene amplification was codetected with HPV DNA in 10/26 lesions, each of them containing at least one potentially oncogenic HPV type (5,16 and/or 18). The amplification was also found in 11/31 cases in the absence of HPV DNA. No significant difference was observed in the detection of HPV or oncogene DNA between the lesions of transplant recipients and those of the non-immunosuppressed population. Viral antigen was detected in 17/55 lesions by indirect immunofluorescence; 5 of the positive biopsies showed ras oncogene amplification. Myc and ras p21 oncoproteins were respectively localized in the nuclei and on the membrane of epithelial cells by indirect immunofluorescence. A good correlation was observed between the amplification of oncogenes and the expression of oncoproteins. Our results favor the hypothesis of a cooperation between HPV infection and myc and ras oncogene activation in skin carcinogenesis.
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PMID:c-myc and c-Ha-ras cellular oncogenes and human papillomaviruses in benign and malignant cutaneous lesions. 131 8

This study examines proto-oncogene hypomethylation in rat livers during the early stages of hepatocarcinogenesis by dietary methyl deprivation in the presence and absence of initiation by diethylnitrosamine (DEN). Male weanling F344 rats were fed a complete diet, or a diet deficient in methionine and choline (MDD). Half the animals in each dietary group were given a single initiating dose of DEN (20 mg/kg). Animals from each of the treatment groups were killed at 1, 3, 8, 16 and 32 weeks, and hepatic DNA was isolated. This DNA was digested with the restriction enzymes MspI and HpaII to determine the extent of methylation of the CCGG sequences in c-Ha-ras, c-Ki-ras and c-fos proto-oncogenes. The results indicate that the administration of the MDD produced hypomethylation of these proto-oncogenes at all times investigated, independent of DEN initiation. The methylation changes in the c-Ha-ras gene increased in intensity throughout the experiment until at 32 weeks they were similar to the patterns seen in both neoplastic and preneoplastic livers of rats fed the deficient diet for 18 months. These results demonstrate that early, selective hypomethylation of some, but not all, CCGG sites occurs in rats undergoing hepatocarcinogenesis by dietary methyl deprivation.
Carcinogenesis 1992 Oct
PMID:The onset of oncogene hypomethylation in the livers of rats fed methyl-deficient, amino acid-defined diets. 133 Mar 45

We immortalized oral keratinocytes by transfection with recombinant human papillomavirus type 16 (HPV-16) DNA and established two cell lines, human oral keratinocytes-16A (HOK-16A) and -16B (HOK-16B). These cell lines were morphologically different from the normal counterpart, contained HPV-16 DNA as integrated form and expressed numerous viral genes. However, these cells proliferated only in culture medium containing low calcium (0.15 mM) and are not tumorigenic in nude mice. To test the hypothesis that tumors can be developed by sequential combined effect of human papillomavirus and chemical carcinogens in the oral cavity, these immortalized cell lines were chemically transformed by exposure to either benzo[a]pyrene or methanesulfonic acid ethyl ester. Such transformants proliferated in medium containing physiological calcium levels (1.5 mM) and demonstrated enhanced growth potential in nude mice, whereas primary human oral keratinocytes treated with these chemical carcinogens failed to show any evidence of transformation. Chemically transformed cells contained integrated, intact HPV-16 sequences and transcribed significantly higher amount of HPV-16 E6/E7 messages and transforming growth factor-alpha (TGF-alpha) compared with the immortalized oral keratinocytes. Like the HPV-immortalized cell lines, the chemically transformed oral keratinocytes contained lower levels of newly synthesized, wild-type p53 proteins compared to normal cells, and expressed wild-type c-Ha-ras. These results indicate that this in vitro system is useful for investigating the mechanisms of multistep oral carcinogenesis.
Carcinogenesis 1992 Nov
PMID:Sequential combined tumorigenic effect of HPV-16 and chemical carcinogens. 133 Mar 48

Pulsed field gel electrophoresis showed that caffeic acid induced DNA strand breaks in cultured human cells in the presence of Mn(II). With alkali treatment, DNA single-strand breaks were observed. The strand breakage was increased by the treatment of buthionine sulphoximine (a GSH synthesis inhibitor) and 3-aminotriazol (a catalase inhibitor) and decreased by catalase, indicating the involvement of H2O2. The DNA damage was decreased by o-phenanthroline, indicating the involvement of transition metal ion. Damage to isolated DNA from c-Ha-ras-1 protooncogene was investigated by a DNA sequencing technique. Caffeic acid caused DNA damage in the presence of Cu(II) but not in the presence of either Mn(II) or Fe(III). Caffeic acid plus Cu(II) induced piperidine-labile sites frequently at thymine residues, especially of the 5'-GTC-3' and 5'-CTG-3' sequences. Typical OH scavengers showed no inhibitory effects. The inhibitory effects of bathocuproine and catalase on Cu(II)-mediated DNA damage suggest that Cu(I) and H2O2 have important roles in the production of active species causing DNA damage. The Cu(II)-mediated DNA damage was enhanced by pre-incubation of caffeic acid with Mn(II). Mn(II)- or Cu(II)-catalyzed autoxidation of caffeic acid produced H2O2 with efficiency of Mn(II) greater than Cu(II). These results suggest that in the presence of Mn(II) or Cu(II), caffeic acid produces H2O2, which is activated by transition metals to cause damage to DNA in vitro and probably in cultured cells.
Carcinogenesis 1992 Sep
PMID:Caffeic acid causes metal-dependent damage to cellular and isolated DNA through H2O2 formation. 139 30

The molecular mechanisms of the carcinogenic process of gastric cancer have not been fully understood yet. In order to know whether c-Ha-ras gene is being involved in the process of gastric carcinogenesis, 8 gastric cancer cell lines, 8 cases of gastric cancer and same number of adjacent dysplasia were analyzed for the presence of mutation at codon 12, 13 and 61 of the c-Ha-ras gene by using polymerase chain reaction (PCR) and mutant-specific oligonucleotide hybridization. Point mutations at codon 12 of the c-Ha-ras gene were found in 2 out of 8 gastric cancer and dysplasia samples in one case, but we found no mutation at codon 13 or 61 of the c-Ha-ras gene. These results suggest that the frequency of mutation of the c-Ha-ras gene detected by sensitive PCR technique is low indeed, however it would be notable that such a genetic change has been detected in the dysplastic lesion of the gastric cancer patient.
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PMID:Point mutation at codon 12 of the c-Ha-ras gene in human gastric cancers. 152 24

The mouse skin model of multistage carcinogenesis has for many years provided a conceptual framework for studying carcinogenesis mechanisms and potential means for inhibiting specific stages of carcinogenesis. The process of skin carcinogenesis involves the stepwise accumulation of genetic change ultimately leading to malignancy. Initiation, the first step in multistage skin carcinogenesis involves carcinogen-induced genetic changes. A target gene identified for some skin tumor initiators is c-Ha-ras. The second step, the promotion stage, involves processes whereby initiated cells undergo selective clonal expansion to form visible premalignant lesions termed papillomas. The process of tumor promotion involves the production and maintenance of a specific and chronic hyperplasia characterized by a sustained cellular proliferation of epidermal cells. These changes are believed to result from epigenetic mechanisms such as activation of the cellular receptor, protein kinase C, by some classes of tumor promoters. The progression stage involves the conversion of papillomas to malignant tumors, squamous cell carcinomas. The accumulation of additional genetic changes in cells comprising papillomas has been correlated with tumor progression, including trisomies of chromosomes 6 and 7 and loss of heterozygosity. The current review focuses on the mechanisms involved in multistage skin carcinogenesis, a summary of known inhibitors of specific stages and their proposed mechanisms of action, and the relevance of this model system to human cancer.
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PMID:Multistage carcinogenesis in mouse skin. 152 55

Lipotrope-deficient (methyl-deficient) diets cause fatty livers and increased liver-cell turnover and promote carcinogenesis in rodents. In rats prolonged intake of methyl-deficient diets results in liver tumor development. The mechanisms responsible for the cancer-promoting and carcinogenic properties of this deficiency remain unclear. The results of the experiments described here lend support to the hypothesis that intake of such a diet, by causing depletion of S-adenosylmethionine pools, results in DNA hypomethylation, which in turn leads to changes in expression of genes that may have key roles in regulation of growth. In livers of rats fed a severely methyl-deficient diet (MDD), lowered pools of S-adenosylmethionine and hypomethylated DNA were observed within 1 week. The extent of DNA hypomethylation increased when MDD was fed for longer periods. The decreases in overall levels of DNA methylation were accompanied by simultaneous alterations in gene expression, yielding patterns that closely resembled those reported to occur in livers of animals exposed to cancer-promoting chemicals and in hepatomas. Northern blot analysis of polyadenylated RNAs from livers of rats fed control or deficient diets showed that, after 1 week of MDD intake, there were large increases in levels of mRNAs for the c-myc and c-fos oncogenes, somewhat smaller increases in c-Ha-ras mRNA, and virtually no change in levels of c-Ki-ras mRNA. In contrast, mRNAs for epidermal growth factor receptor decreased significantly. The elevated levels of expression of the c-myc, c-fos, and c-Ha-ras genes were accompanied by selective changes in patterns of methylation within the sequences specifying these genes. Changes in DNA methylation and in gene expression induced in livers of rats fed MDD for 1 month were gradually reversed after restoration of an adequate diet. In hepatomas induced by prolonged dietary methyl deficiency, methylation patterns of c-Ki-ras and c-Ha-ras were abnormal. Although human diets are unlikely to be as severely methyl deficient as those used in these experiments, in some parts of the world intake of diets that are low in methionine and choline and contaminated with mycotoxins, such as aflatoxin, are common. Even in industrialized nations, deficiencies of folic acid and vitamin B12 are not uncommon and are exacerbated by some therapeutic agents and by substance abuse. Thus, it seems possible that interactions of diet and contaminants or drugs, by inducing changes in DNA methylation and aberrant gene expression, may contribute to cancer causation in humans.
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PMID:Methyl groups in carcinogenesis: effects on DNA methylation and gene expression. 154 43

Our earlier studies had demonstrated that inhibition of DNA methylation following carcinogen treatment potentiated initiation of the carcinogenic process in the rat liver system. The hepatic nodules developed by initiation-promotion protocols showed a characteristic hypomethylation in the cell-cycle-related genes c-fos, c-myc and c-Ha-ras. In the present study we have found that the gene for beta-hydroxy-beta-methyl glutaryl coenzyme A reductase, a major rate-limiting enzyme in the biogenesis of mevalonate, is also hypomethylated at both CCGG and GCGC sites and expressed in hepatic nodules. This gene, however, did not exhibit hypomethylation in CCGG sequences in non-nodular surrounding liver, livers from rats subjected to two-thirds partial hepatectomy, or exposed to initiator alone (1,2-dimethylhydrazine given 18 h after partial hepatectomy) or to diets containing 1% orotic acid alone (promoting regimen). The activity of the enzyme and mevalonate formation are positively correlated with DNA synthesis and cell proliferation--two key components of the carcinogenic process. Taken together, the results suggest that hypomethylation of specific genes occurs in the carcinogenic process and this altered pattern of DNA methylation may play a role in the growth of the nodules.
Carcinogenesis 1992 Mar
PMID:Hypomethylation of beta-hydroxy-beta-methyl-glutaryl coenzyme A reductase gene and its expression during hepatocarcinogenesis in the rat. 154 42


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